1. Field of the Invention:
The present invention relates to a pneumatic pumping device in which a movable valve performs reciprocating movement by using air back pressure, and pumping operation is carried out by the reciprocating movement.
2. Description of Prior Art:
Hitherto, there has been proposed a pneumatic pumping device in which a bellows performing reciprocating movement by back pressure of air is disposed in a cylinder so that a liquid is drawn in and discharged by the reciprocating movement, as is disclosed in Japanese Patent Official Gazette under Publication No. 56-50116 and Japanese Utility Model Laying-Open Official Gazette under Laying-Open No. 61-29078.
In such a conventional pumping device, two bellows are respectively disposed in both left and right cylinder chambers, the bellows being connected with each other through the piston rod, so that when one bellows moves either forwardly in one direction or backwardly in the returning direction by the application of air back pressure, such movement is transmitted to the other bellows through the piston rod to make the other bellows move forwardly or backwardly, thus pumping operation takes place by such reciprocating movement of the bellows.
In the conventional pneumatic pumping device of the aforesaid construction, there are provided on the outer part thereof connecting members such as fittings for connecting pipes with an intake port and a discharging port of the cylinder; bolts and nuts for assembling the cylinder, bellows and other components; and mettalic members for providing rigidity to the components of the pump.
Accordingly, when the conventional pumping device is used in a liquid of strong acid or strong alkali, it becomes soaked and the aforesaid connecting members, bolts, nuts, metallic components, etc. become corroded, broken down and out of operation.
Furthermore, the conventional pumping device is necessarily composed of a pair of horizontally disposed pumps, so that contruction of a small-sized pumping device becomes substantially impossible.
Moreover, when the pressure associated with the feeding of a chemical liquid and the heat thereof generated by the chemical reaction are applied to the components of the pump, there arises a problem of stress relaxation at joining sections of the components. Accordingly, a gap may come out at the joining section between the bellows and the cylinder, otherwise a compressive creep may attack O rings and the like provided to maintain a sealing function, resulting in a decline of such function.
Another type of pumping device is disclosed in Japanese Patent Official Gazette No. 48-20807, and according to which the pumping device is driven by hydraulic pressure and therefore hydraulic driving means such as a hydraulic pump are needed, which makes the construction rather complicated.